The objectives of this research program are to analyze the organization of monoamine neuron systems in the mammalian brain and their response to injury. In the work to be carried out during the coming year we shall analyze the development of monoamine neuron systems innervating the rat brain stem. This will be carried out concomitantly with an analysis of the effect of neonatal administration of 6-hydroxydopamine on the development of catecholamine neuron systems in the rat brain. Further studies will be directed toward analysis for the noradrenaline neuron innervation of the hippocamal formation and, in particular, an analysis of the ultrastructue of terminals innervating hippocamal formation. A further study will reevaluate the response to catecholamine neurons innervating the rat septal area to denervation of the septum by removal of hippocamal afferents traversing the fornix. The overall objective for the current year is to extend our information concerning the organization of catecholamine neuron systems innervating mammalian brain and the capacity of these systems to exhibit plasticity in response to injury in the developing and in the mature nervous system.